1. Field of the Invention
This invention relates to an image forming apparatus such as a laser beam printer, an electrostatic photocopier, or the like, and more particularly concerns an image forming apparatus which incorporates an improved light eraser for removing electric charges from a photoconductive member.
2. Description of the Related Art
In a typical image forming apparatus such as a laser beam printer and an electrostatic photocopier, an electrostatic latent image is formed on a photoconductive member overlying the outer peripheral surface of a rotating drum, which is then followed by (a) a toner development process in which particles of toner powder are adhered to the photoconductive member, (b) a transfer process in which a toner pattern on the photoconductive member is transferred onto a copy paper sheet, and (c) a fixing process in which the transferred toner pattern is affixed to the copy paper sheet. Thereafter, as preparations for the next image forming process, residual toner powder particles remaining on the photoconductive member are removed therefrom and the surface of the photoconductive member is illuminated with light rays from a light eraser located face to face with the photoconductive member so that residual electric charges remaining in the photoconductive member are optically removed.
A light eraser is required to illuminate light rays across the entire width of a photoconductive member. For the case of a full-color photocopier having a plurality of photoconductive members, it is necessary to illuminate light rays across the entire width of each of the plurality of photoconductive members.
a) FIG. 4 shows a prior art technique (i.e., a light eraser 102) for applying light rays across the entire width of a photoconductive member, wherein a plurality of light-emitting diodes (hereinafter called the LEDs) 104 or a plurality of incandescent electric lamps serving as light sources are mounted on a substrate 103 in a side by side fashion in the axial direction of a photoconductive member 101. However, the problem with the light eraser 102 is that the LEDs 104 are likely to vary in performance, resulting in illuminating the photoconductive member 101 at different quantities of light. Therefore, the photoconductive member 101 cannot uniformly be discharged across its entire length. In order to avoid such a drawback, it has been proposed to employ a light receiving element 105 such as a photosensor for detecting the quantity of light. However, it is practically difficult to measure the quantity of light for each LED 104 because of some constraints such as limitations of space. Additionally, since the number of component parts increases, this will establish limits to improving durability as well as to reducing manufacturing costs.
b) In a full-color photocopier of a tandem type, a plurality of photoconductive members are each provided with a light eraser. Recently, with the downsizing of electrophotographic copiers, the size of photoconductive members is likewise reduced. Accordingly, it is necessary to reduce a space between devices (e.g., cleaners and chargers) mounted in the vicinity of a photoconductive member. It is therefore difficult to achieve the downsizing of photoconductive members when an LED unit as a light eraser is provided to each photoconductive member. The reason is that, when an LED unit is disposed around the periphery of a photoconductive member, space must be secured for the LEDs and a substrate.
Use of optical fibers may provide solutions to these problems with the prior art techniques. More specifically, in order to solve the problem a), a single light source 104 such as a lamp for electric charge removing is mounted and an optical fiber 201 is disposed such that it runs along specified portions of the photoconductive member 101 from the light source 104 as shown in FIG. 5. Formed on the outer peripheral surface of the optical fiber 201 on the opposite side to the photoconductive member 101 are a diffusion area extending along the longitudinal direction of the optical fiber 201 and a reflection area exterior to the diffusion portion. In such an arrangement, rays of light (L) from the light source 104 are reflected or diffused in the radial direction of the optical fiber 201 so that the specified portions of the photoconductive member 101 are illuminated for optically removing residual electric charges (see S62-127786).
In such a configuration, the single light source 104 applies the light L to the photoconductive member 101 through the optical fiber 201. The use of the configuration, however, increases component part costs to a great extent because optical fibers are relatively expensive. Moreover, since the optical fiber 201, when used as it is, is unable to diverge the light L toward the specified portions, the configuration in point has the disadvantage of lacking in latitude with respect to the guiding of the light L of the light source 104 toward the specified portions.
Also, for the problem b), it may be considered that a simplified apparatus configuration is accomplished by making utilization of an optical fiber so as to guide light rays from a single LED unit toward a plurality of photoconductive members. However, such arrangement is difficult to make for the same reason as described previously, and is costly.
To solve both the problem a) and the problem b), a waveguide member capable of easily achieving divergence, refraction, and transmission of light rays is required. By the use of such a waveguide member, it becomes possible to reduce the number of light sources required and, further, as for the problem a), it is possible to evenly apply light rays across the entire width of a photoconductive member.